Radio object locating training device with error indication



Dec. 27, 1949 O, CESAREO 2,492,356

RADIO OBJECT LOCATING TRAINING DEVICE WITH ERROR INDICATION Flled Deo. 6, 1943 5 Sheets-Sheet 1 Dec. 27, 1949. o. CESAREO 2,492,356

' RADIO OBJECT LOCATING TRAINING DEVICE WITH ERROR INDICATION Filed Dec. e, 1945 5 sheets-sheet 2 O. CESAREO RADIO OBJECT LOCATING TRAINING DEVICE WITH ERROR INDICATION Dec. 27, 1949 5 Sheets-Sheet 5 Filed Dec. 6, 1943 www.

VEA/TOR 0. CESARE 0 A Tron/V5 y Dec. 27, 1949 o. CESAREO 2,492,356

RADIO OBJECT LOCATlNG TRAINING DEVICE WITH ERROR INDICATION Filed Dec. 6, 1945 5 Sheets-Sheet 4 /N VEN TOR y O CESARE 0 A r rom/EV Dec. 27, 1949 O, CESAREO RADIO OBJECT LOCATlNG TRAINING DEVICE WITH ERROR INDICATION Filed Deo. 6, 1945 5 Sheets-Sheetr 5 Patented Dec. 27, 1949 UNHTED TES PATENT AFFE Y(2E Orfeo Cesareo, Washington Township, .Bergen County, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, LN. Yi.,

corporation of New York Application December 6, 1943, Serial1No.:-51'3',044

v4 IClaims.

il -This-.invention relates to signaling systems and apparatus andparticularily to systems for training students in the art oflocating distant objects. Systems `'have been devised 'for determining Athe range and angular 'location of an airplane or other object moving at a variable speed .in space. These locating systems make use of directive radio `impulses which .are transmitted .from the point of observation to the movingairplane, from which they return as .echo impulses. The returning impulses .are received and utilized to form images on a screen before the operator, and the character and behavior of these images faiord a continuous representation of .the .range ,and angular location of the .moving airplane. The operator is also .provided with adjustable means, such vashand Wheels, which he manipulates to follow yor otherwise control these .changing images. Devices responsive .to thek operators hand wheels as .he follows or tracks .the moving airplane .provide the necessary information for training guns on the airplane asa target.

'Training systems have also been devised for giving students a Vpreliminary `course .of `training in the art of manipulating the `object .locating systems. vTo .this end the courses of .imaginary airplanes are generated automatically in terms-of varying electrical quantities representative oi range and angular dimensions and these varying electrical quantities .are used .to .produce images on a screen before the student corresponding 'to those which the operator observes when engaged.. in tracking areal airplane. The student is likewise provided with manually .operable devices, such as hand wheels, which he manipulates to simulate'the act of following the imaginary object. The illusion vaiordedby these training systems is quite effective, `and prictice in manipulating them soon develops the .students skill. It .has been recognized, however, that the usefulness of the training system would be largely Ienhanced Aby provision of some means .for detecting A and measuring the error Yof 4the students.

'Objects ofthe invention, therefore, are lto detect the presenceof -error `on the part of thestudent in following the movement .of an imaginary object in space.; to establish varying standards in proficiency; to observe the students error either when following .the range or the angular l'location of the moving-object; .and .in other respects to improve systems-of this general character.

These and other objects Aof .the invention are realized `by means 4of asystem in which 'the signa'ls representing .the location of the y.imaginary course being generated .are compared with l.the signals which the student controls in his effort to follow themovemento'f 4the imaginary object. More specifically, 'the range `and the angular .dimensions of Lthe imaginary .course generated 'by the training system .are .represented by varying the phase of alternating waves taken tfrom a Vbase source. 'The .student endeavors to .follow either the range .or .the .angular .relation 'by ,introducing intosaid .wavesmanufally similar variations .of phase, andthe presence o'ferror on .the part .of the student, either while tracking the .range or the angular location oi the imaginary object, is determined by comparing the phases o'f impulses derived from said waves. .If at any instant the impulses derived vfrom the .wave .controlled .by the course generator are in phase with Athe rimpulses derived .from ,the wave controlled'by the students phase shifter., these vimpulses .add .and the result is that the .mechanism operates in a manner to indicate that the student .is .on the target. Ii, however, these .impulses .do not occur concurrently, thestudent is in error, and .the ,mechanism so indicates.

With .this .arrangement .it is .possible to require the students to .demonstrate varying degrees of proiiciency .in order Lto be free from error. 'For beginners .a .low .proiic-iency .isrequired and this is achieved byfincreasing -`the `time duration of either oneorboth ofthe matchingimpulses. The longer the impulse the more latitude the student has in Vthe manipulation .of .his .tracking Amechanism. On Ithe other. hand themore skilled .students are .subjected lto ahigher standard .by .shortening the .length oi" vthe .impulses wich .they must .bring into synchronism .in .order .to prevent .the mechanism fromrecording error against them.

The foregoingand .other fea'tures of the invention will be discussedmoretully in .the following detailedspecication.

In the .drawings accompanying the speciiication:

Figs. l, 2, l3 .and-4, when `arranged .in order. constitute a diagram .of .a training system incorporating the features iof the invention.;

l'igA .-1 shows .a part .oi the course .generating equipment associated with the .instructors position;

Fig. 2 illustrates the equipment associated with a -studentfs position, including the 4students phase shifter .and the oscilloscope in which he observes the moving images;

4lili-gs. 3 and -4 disclose thefcircuits .and apparatus for detecting and indicating the students error;

Figi .5 is. a fragmentary view :illustrating the :azimuth images on the oscilloscope screen;

Figs. 6, 7 and 8 are diagrams illustrating the formation and matching of impulses for detecting the students error; and

Fig. 9 illustrates the instructors apparatus cabinet and one students apparatus cabinet as they would be set up for training purposes.

The three dimensions of primary interest in the location of a moving object, such as an airplane, are range, azimuth angle, and elevation angle; and the rst requirement of a training system for students is to generate in terms of suitable electrical quantities artificial or imaginary courses of flight in which these range and angular dimensions vary in the desired manner. In the copending application of Andrews and Cesareo, Serial No. 519,042, filed December 6, 1943, which issued April 6, 1948, as Patent No. 2,438,888, a training system is disclosed in which straight-line courses are generated having varying values ofV range and azimuth angle, in which images are formed on the students .oscilloscope representing the varying range and azimuth angle, and in which the student is provided `with means which he can manipulate to track or follow either the range or the azimuth angle of the imaginary object moving along theY simulated course. In this Andrews and Cesareo patent the instant values of the range and azimuth angle are represented on the oscilloscope screen by means of triangular shapedimagesor pips. One of these images moves on .the screen with respect to a stationary notch, also `formed thereon, and the student tracks the range of the imaginary object by manipulating his devices to hold the image pip located in the stationary notch. The azimuth angle on the other hand is represented on the oscilloscope screen by means of a pair of these triangularshaped images .which are located in the center of the screen in associated notches. Although these image pips remain stationary throughout the generation of the imaginary course, they varyin their altitude in accordance with variations in the azimuth angle of the imaginary object, andthe student endeavors to manipulate his control device in such a manner as to maintain these images at equal altitudes. As long as he is able to do this, heV is accurately following the azimuth angle of the imaginary object.

In the system of the present invention the accuracy with which the student manipulates his control device either while following the range or the azimuth angle is under constant surveillance by circuit means which compares the phases of the waves utilized in the formation and control of the images on the oscilloscope screen and from these comparisons determines` and records all errors made. Fora better understanding of the system reference is now made to the drawings.

The apparatus at the instructors position is mounted in an apparatus cabinet 990, shown in Fig. 9, having front closure doors 99d and 992 and a control panel 903. The sides of the cabinet are provided with ventilation slots 904 and with cable jacks, such as 905, by which the cabinet may be connected with one or more students positions. The apparatus at a students position is mounted in an apparatus cabinet 9%, shown in Fig. 9, having front closure doors 997 and 908, a panel 999 on which an oscilloscope and controls therefor are mounted1 and a control panel 9H). The sides of the cabinet are provided With ventilation slots 9H andv with ca ble jacks, such as 912, by which theV cabinet mayY be connected by plug-ended cables 953 with the instructors apparatus cabinet 999 and with other students cabinets similar to cabinet 996.

The ight generator, which is only partially disclosed in Fig. l, may be of the same type as the one shown and described in detail in the copending application of D. I-I. Pennoyer, Serial No.

`513,076, led December 6, 1943, which .issued April 6, 1948, as Patent No. 2,438,940. It includes a motor |00 for driving a range phase shifter lill which introduces into an alternating `Wave taken from the base source 492 a change of phase, the instant value of which represents the range of the object with respect to the point of reference. It also includes a motor l 03 for driving the azimuth phase shifter |04 which introduce into a wave taken from the output circuit of phase shifter il?! a change of phase, the instant value of which represents the azimuthsangle of the imaginary object. The Vcourse generator also includes-.suitable control mechanism iiibyY which the. instructor can preselect the desired course ,to be generated, and a flight motor 96 and associated control circuits for driving and controlling, the generating,mechanismrafter the instructor .has made the desired setting.

E'ach students position is .equipped with an oscilloscope 299 having a luminescent screen on which a horizontal trace 2li! is formed .with a stationary center notch 292 therein having a movable image pip 293 which represents the range of the imaginary object. While the student is tracking theV rangeV of the imaginary object, he endeavors to manipulate his phase shifter 294 to control in such a manner the phase of the wave forming the image pip .293 that the pip rests accurately in the notch 292. If, on the other hand, it is desired to have the student follow the azimuth angle the keys E98, 295, 22 Ztl and 298, all of which may be controlled by a single lever or button at the instructors position are moved to their alternate circuit positions; and the student now observes a pair ofimage pips 599, (Fig. 5) located in corresponding notches in the horizontal trace 5.92 which vary in their relative altitudes in accordance with the varying azimuth angle of the imaginary object in space. To trace the azimuth angle, therefore, he similarly manipulates his phase shifter 294 in an effort that the student is free from error in the manipulation of his tracking devices. In other words, as long as the student is ongthe .target either with respect to range or azimuth the clock 4H runs.'

By comparingrthe reading ofthe students clock 4i lV at the end of a flight with the reading of a standard clock Eilat theinstructors position, which runs continuously from the beginning to the end of the ight, the total error timeV chargeable against the student may be calculated.

Examining the circuits of the system more closely and assuming for the moment that the keys are in the positions shown, namely the positions for range tracking, it will be noted that a wave of the base phase and frequency from the source H12, after undergoing amplification by a suitable amplifier HB9, is applied to the phase shifter l0! of the course generator. The resulting phase-shifted Wave in the output circuit of shifter l lll is amplified by amplifier l l Il and is then con-l ducted over circuit I Il to the rectifier 209. VThe Duisesresulting .from the rectified waveareguti- 'lized by pulse Agenerating.and.-svveep .control cirw cuits 2|.0,.;2.|.| of .Wellknown-types-tocontrolthe beam-.of theoscilloscope-200 to form the horizontal 4trace20| in -synchronism with the phaseshifted wave. At the same .time a .wave from the output .of .the phase -shifter -|0.| .is subjected to a constant .shift of -90 -degrees -by .a suitable `circuit |f|2.and islthen applied-,over-conductor ||3 to the rectierll2. The resulting rectied impulses are applied -to a .pulse inverter 2l-3, -and .the inverted impulses are utilized by .an impulse generating circuit 2.|4 .to produce the notch 2 02 in the ,horizontal .trace 20|. In view .of the.90degr.ee1rela tion .between .the phases :of the wave which .produces the -`trace and thewave which produces the notch this notch will remain stationary on the screen and will .be `located in the 'center thereof.

`...Also .a Wave .taken :from the -basesource |02 .is applied ,over conductor E4 through the `contacts of Ykey |108 tothe students phase shifter 204. .The output. wave from fthe .phase :shifter 204 is applied .over the .circuit through keys 205 and 2.00 vto the .impulse rectifier 215, 'Ihefimpulses after rectification .are ,inverted by means of .a suitable pulse inverter 21.6 vand are then kapplied -to the impulsegeneratingandshaping circuit 2| 1. The output ,impulses .from the circuit 217| are amplied Y.by a suitable :amplifier -2|3 and are then applied .to the vertical-.deflection plates -22-9 and 230 of .the .oscilloscope .200. Neglecting Athe .effect -.of thestudents phaseshifter 2104it-will .be seen that the impulses appliedv tothe vertical plates of the oscilloscope ,200 .are .in phase with the original source .|-102.; therefore, .the image 4pip 2.0-3 -vvhich .is formed by .these impulses .inthe horizontal trace 211| .will appear .to-move across .the screen in -accordance with .the chang-ing -phase introduced by the .range l.phase shifter ..|.0,|. Noting .the fmovement .of the image pip .-203 .and its location-suchas that indicated .by .thevdotted pip 21|9, thestudentmanipulates .the .phase shifter .-204 to :introduceintmthe wave .that forms .the pip 20.3 aphase change .which is Just .suilicient to advance the pip into juxtaposition .with the notch 202 and -to :hold it there.

`Flor-.each.instant that :the student :is-able @to -ho'ld the z-pip 203 reenter-ted iin .the .notch 202 .the impulses appearing in-conductor 220 are exactly 'in phase with the impulses appearing in iconductor 22|. .This sis -.true .because .the :impulses in 4iconductor ..220 are those .which "form the Afimage203 and .the :impulses in conductor 22| .are those which form .notch .202. Therefore, fa comparison =of the phases of these :impulses shows mo phase diierence, :and this .-fact may 'tbe :taken asian .indication `that the student is .not :making any error. vSuch :a comparison is made :by the circuits shown in Fiss. .8 and .4.

The .alternating awave in circuit |i3, after being rectified :and inverted by =the-rectifier and inverter circuits 2.12 :and 12| 3, ithe appearance illustrated in :Fig a6. fBy properly choosing the bias :of .the :tubes used in the inverter zcircu'it, the

rectified wavez|i|l0 islclippedfand onlyetheiimpu'lses 601 :602, 603, reto., :appearing `alcove .the :axis .are permitted to .ow :into `the circuit 22|. itis explained labove, :these impulses are rapplied to `.the generator Y2ML, which :shapes v.them and utilizes them Yto form athe ,notch in .the :trace 20|.. 'These 30.4..;issnormally `biased negatively by the zbattery 305 `the .extent of .the -bias .depending uponthe position -of .the potentiometer contact. When, therefore, the., positive impulses 602, z603, -.etc which .are in exact synchronism .with the .impulses 'forming .the reference 'notch 202 v.on `the screen, .areapplied `to the vgrid element 303,.they oppose .the normal bias, Aand the tube 304 -conducts. ,The-:functionof the tube 304 ,is tolreform the sharp impulses received over circuit222 and to lgive them .a square shape ras indicated :by the impulses 6.04, |505, :606, fetc. Since the Width-.of the reformed impulse 604 is Ydetermined by the conducting time of the tube 304, the bias applied to the control grid 303 may be utilizedto vary-the widthof the impulse. The impulses arriving over circuit 222.;are of uniform ,width, and rfor agiyen bias .on the grid ..303 the impulses vin :the output circuit of .the tube 304 will have a iixedfwdth, such as that .illustrated for .the impulses l004, .605. 606, etc. To .increase :the widthof the reshaped impulses vit .is .only necessary to adjust .the potentiometer A302 to decrease the negative bias :on the grid 30,3. .Decreasing the negative biasincreases the .time during which .the .tube .304 Lconducts for each. .successive impulse, thereby increasing the width of the reformed impulses 601,000, A||)9,etc. If on the other Vhandit is desired .to-decreasethe width .of lthe .reformed impulses, thenegative bias is .increased to .reduce .the conducting time for each impulse, -and .the result :is that lthe reshaped impulses iii-0, B-Ijl, 6.|2, etc., are reduced in width correspondingly. The .anode-cathode circuit for the tube 304, in which the reshaped impulses appear, may be tracedfrom .the positive vpole ofbattery 306, resistors 301 and308, `anode 309, cathode 3|,0 to ground. The suppressor grid 3,|:| Vis ,connected directly to ground, andthe screen grid 3|2 is .maintained at a positive potential by the battery 3|3. The condensers 3|4 and 3|5are inserted for filtering purposes. Whilea considerable squaring effect is obtained with-the single tube 304, this .effect may .be enhanced by adding a second stageof shapingand this is done by means of the succeeding tube .3|0. The impulses inthe output circuit .of tube 304 are applied through condenser 3|'I -to the resistor 3|0 for effecting correspondingly .the control grid of the tube `3|6. The finally shaped impulses in `the anode circuit of the tube 3|.6 .are applied through condenser 3| 9 to the circuit l320.

Concurrently with the formation of these square-topped impulses in phase with theim pulses which yform the reference notch 2.02 on the screen, similar pu-lses are formed bythe tubes 32| and 322 in .phase with the impulses which, under the control of the students phase shifter 204.cause the formation of .the range image ,pip 203.. To this end the inverted impulses in the-.output Vcircuit of inverter 2 I6 areconducted over cir cuit ..223 .through the key .201, conductor 224, through condenser 323 and resistor 324 to the potentiometer 325. These impulses are applied to tube 32| which partially shapes them, Yand the output impulses from this tube are applied to the second tube 322 which completes the shaping ,op-

eration and delivers to the conductor 320 by way of .conductor326 square-topped impulses in phase with the impulses forming the image .pip 203. By similarly controlling the negative bias .applied to the control grid of the 'tube 32| with the necessary adjustment of the potentiometer 32.5 it is possible to "select any desired Width for the .impulses flowingover 'the circuit 320 tothe common circuit 320. v

'The -cornmon conductor 3 210 is connected to `the control grid V400 -of `tube 405| a-ndthrough reaaeasae sistor r,402 to the potentiometer 403. The potentiometer 403 is set to apply to the control grid 400 a normal negative bias from the battery 404 which is sufficient to prevent the tube'40l from conducting when positive impulses are delivered to conductor 320 from either one alone of the tubes 3 6 and 322. For example, if the student is in substantial error in his effort to follow the range of the imaginary object, meaning that the image pip 203 is out of the notch 202 on one side or the other, the impulses 100 (Fig. 7), which are formed by tubes 32| and 322 in phase with the impulses which form the image pip 203, are substantially out of phase with the impulses formed by the tubes 304 and 3 I 6 in phase with the impulses that form the reference notch 202. Therefore, these positive impulses 100 and 10| are applied to the grid 400 sequentially and do not reduce its bias sufficiently to permit tube to conduct. As long as the tube 40| is non-conducting the negative bias applied from battery 405 through resistors 40S and 401 to the circuit of the control grid 408 and cathode 409 prevents the tube 4|0 from conducting. Therefore the clock 4|| fails to run, indicating that the student is in error at this time.

As the student brings the image pip 203 back toward the notch 202 the error detecting impulses 102 and 103 approach each other until finally, as the error is minimized, these impulses coincide in point of time, as indicated by the superimposed impulses 104-105 and 10B-101. Since these impulses are now concurrent in time, they add in the circuit 320, the tube 40| conducts,

and current flowing in the resistor 4|2 decreases the negative bias on tube 4 0 permitting this tube also to conduct. Current flowing from the battery 405 through the operating coil 4|3 and the anode and cathode of the tube 4|0 causes the clock 4|| to operate to record the accurate manipulation by the student. The condenser 4|4 is included in the cathode circuit of tube 40| and assumes a charge in response to a succession of conducting intervals by the tube. The condenser 4|4 and the resistor 4|2 are suitably proportioned to enable the tube 4|0 to respond accurately to the matching impulses delivered to the input circuit of the tube 40 Y From the foregoing it will be seen that the student is considered to be in error at all times when the impulses applied from tubes 3|6 and 322 to the common conductor 320 do not overlap and add to each other, and during these times the error recording c-lock 4|| fails to run, Since, therefore, the student is considered to be free from error or on the target at all times when these impulses are suiciently in phase to overlap and add to each other, it is possible by varying the width of the image impulses to increase or decrease at will the degree of accuracy with which the student must manipulate the tracking mechanism in order to keep himself free from error. This method of varying the standard of proficiency is clearly illustrated in Figs. '7 and 8. If, for example, a student is a beginner, he may be given the benefit of a lower standard by adjusting the potentiometer 302 for the maximum width impulses 10|, 102, 104, 106, etc., in the output circuit of the tube 3|6. These impulses, being of maximum width, make it that muc-h easier for the student to bring the impulses in the output circuit of tube 322 into overlapping relation therewith. This overlapping relation is illustrated in the last two positions of Fig. '7. In the first of these positions the impulse 105 controlled by the 8 students phase shifter 204 is shown overlapping the edge of the pedestal impulse 104 but the overlapping portions add to each other, giving a total voltage sufficient to operate the tube 40| and cause the clock 4|| to run. This would correspond to a rough registration of the image pip 203 with the notch 202 as' distinguished from an accurate centering of the pip in the notch. In the last position of Fig. '7 the students impulse 101 is seen to be more closely in phase with the pedestal impulse 105, and, as before, the clock 4|| is caused to run to credit the student with ontarget operation. Thus, if the student is able to maintain any substantial portion of his impulse in an overlapping relation with any portion of thewide pedestal impulses he is able to keep the clock running. On the other hand, the more skilled student should be subjected to a higher standard of proficiency, and this may be accomplished by varying the bias on the tube 304 to k reduce the pedestal impulses 000, 30|, 802, 803,

etc., to their minimum Width. In this case it will be more diflicult for the student to maintain the matching impulses 804, 805, 806, 801, etc., which he controls, in an overlapping or adding relation with the pedestal impulses.

It will be understood, of course, that the standards of proficiency above described may be controlled either by varying the width of the pedestal impulses with the potentiometer 302 or by varying the Width of the student controlled impulses with the potentiometer 325 or by varying the. width of both of these impulses.

At the commencement of the imaginary flight,

- the azimuth of which the student is tracking as above described, the off-normal switch ||6 is operated in any suitable manner by the ilight' motor |06 to close an energizing circuit for the standard clock I5. This clock runs continuously throughout the period of the flight and is stopped at the end of the flight by any suitable means for opening the switch I6. A comparison, therefore, between the total time of the flight indicated by the clock 5 and the total time of accurate,`

nism 225 effective, and the result is that alternate I sweeps of the oscilloscope beam are spaced to give the effect of two notches instead of one located side by side in the central portion of the screen, as seen in Fig. 5. Furthermore', the key` 206, now being in its alternate position, a wave taken from the output circuit of the phase shifting device ||2 is applied to the impulse rectifier 2 I5. The resulting impulses, after being inverted, shaped and suitably amplified, are applied to the vertical plates of the oscilloscope to form at each sweep of the beam an image pip which is accurately located Within the concurrently formed notch, resulting therefore in the appearance' of two image pips 500 and 50| on the screen of the v oscilloscope. One method by which these images are spaced is disclosed in detail in the abovenoted Patent No. 2,438,888 of Andrews and Cesareo.

The two image pips 5,00 and 50| thus formed f side by side on the screen from the wave taken froini the output! circuit of amplifier' lm unless subjected to the iniiuence ot the course geerator, remain at equal amplitudes. However, it is the relative change in the amplitudes of these images that denotes to the student the changing azimuth angle ofthe imaginary object' which lie) is supposed to-follew-. To Aee'c't this"L elia-fige awave taken` from--the Y outputl circuiti of "the amplifier is applied to the azimuth phase shifter IBB of the course generator which introduces therein a change of phase representative of the changing azimuth angle of the imaginary object. The output from the phase shifter |04 is now applied through the contacts of key |68 to the students phase shifter 2M, and the output wave from the students phase shifter 264 is applied over the contacts of key 295 to the amplifier 226 from whence it is applied over conductor 221 to the pulse generator circuit 2 i 'I'. If the wave thus applied from the amplifier 2255 to the pulse generator 2H is exactly in phase with the wave applied to the generator over conductor 220, it does not affect the impulses which produce the image pips 59E and Elli. However, if the Wave applied over conductor 272i is not in phase, indicating that the student is not tracking the azimuth angle accurately, it reacts on the pulse generator circuit 2liu causing one of the image pips EMI- 553| to increase its altitude and the other to decrease its altitude. The manner in which this phase difference affects the pulse generator 2|? is disclosed in detail in applicants copending application Serial No. 513,043, filed December 6, 1943, which issued as Patent No. 2,453,- 743 on November 16, 1948.

From the foregoing explanation of the manner in which the azimuth angle is followed by controlling the altitudes of the images 500 and 50| on the screen it will appear that the students error in following the azimuth angle may be detected by making the same comparison, described in connection with range tracking, between the phases of the impulses appearing in conductor 22| and the phase of the impulses appearing in conductor 221. The impulses in conductor 22| are, as before, delivered over conductor 222 to the tubes 304 and 3|6, and in the present case, the key 267 being operated, the impulses in conductor 22'! are delivered by way of conductor 224 to the tubes 32| and 322. It follows, therefore, that the clock 4|! will run at all times when the impulses formed in the output circuit of tube 3|6 are in overlapping relation with those formed in the output circuit of tube 322 and will remain quiet at all times when these impulses are not in overlapping relation. As the development of the course proceeds the student manipulates his phase shifter 204 endeavoring to maintain the image pips 50S and 50| at equal altitudes, and as long as he is able to achieve this result within the limits of the proficiency standard assigned to him the clock 4H continues to run to credit him with accurate tracking. In this case, too, the standard of proficiency may be varied by varying the width of one or the other or of both sets of image impulses.

What is claimed is:

l. In apparatus for training in locating the course of an object moving in space the combination of a screen visible to the operator of said apparatus, a source of alternating current, means for utilizing waves from said source to form on said screen images which vary in accordance with a dimension of said moving obsacaste ject with'respect tofa point ofreference, said? images Yserving to guide the operator infollowing said object@l track-ing means manipulated'.v bythe operator for controlling the relationship of said'ima'gs in his effort to follow said dimension;- error indicating means effective whenever the operator fails to manipulate said tracking means with siiiiici'et accuracy to follow said dimension, and means for varying the degree of accuracy required of the operator to prevent said error indicating means from becoming effective.

2. In a training device having means responsive to waves from a source of alternating current for electrically simulating images corresponding to the changes in position of an artiiicial target, said images serving to guide an operator in following said target, tracking simulating means manipulated by the operator for shifting the phase of one of said waves, a rst electronic means responsive to one of said waves, a second electronic means responsive to the other of said waves the phase of which has been shifted by the operator, other electronic means responsive to the outputs of said first and said second electronic means during intervals when the phases of their outputs match as a result of no error of the operator in following the target. and means controlled by said latter electronic` means for indicating the total duration of said intervals.

3. In a training device having means responsive to waves from a source of alternating current for electrically simulating images correresponding to the changes in position of an artificial target, said images serving to guide an operator in foilowing said target, tracking simulating means manipulated by the operator for shifting the phase of one of said waves, a rst electronic means responsive to one of said waves, a second electonic means responsive to the other of said waves the phase of which has been shifted by the operator, other electronic means responsive to the outputs of said first and said second electronic means during intervals when the phases of the impulses of their outputs match as a result of no error of the operator in following the target, means controlled by said latter electronic means for indicating the total duration of said intervals, and means for changing the response of either one of said first or second electronic means for varying at will the time duration of the impulses of its output to vary accordingly the accuracy required of the operator to be free of error.

4. In a training device having means responsive to waves from a source of alternating current for electrically simulating images corresponding to the changes in position of an artiiicial target, said images serving to guide an operator in following said target, tracking simulating means manipulated by the operator for shifting the phase of one of said waves, a rst electronic means for deriving a first series of square-topped impulses from one of said waves, a second electronic means for deriving a second series of square-topped waves from the other of said waves the phase of which has been shifted by the operator, other electronic means for matching the phases of the impulses of said two series to determine whether or not the operator is in error, means controlled by said latter means to indicate the total of the intervals when the operator does not err in the manipulation of said 11 I 12 phase shifting means in following the target REFERENCES CITED with the required accuracy, and means for Y changing at will the time duration of the mmlf mmggferens are of record in the pulses of either one of said series to vary accordingly the accuracy required of the operator 5 UNITED STATES PATENTS to be free of error. Number Name Date 1,939,706 Karnes Dec. 19, 1933 ORFEO CESAREO 2,321,799 cone June 15, 1943 2,399,661 Bowie May 7, 1946 

